1. Field of the Invention
The present invention relates to torque wrenches, and in particular, to a hand-operated electronic wrench employing an electromechanical release that is triggered by adjustable torque and/or angle measurement parameters.
2. Description of the Prior Art
Hand operated torque wrenches are commonly available in many configurations, including simple bending beam, dial, preset and adjustable click, and electronic signaling types. The simple bending beam wrench is grip-sensitive thereby requiring the user to maintain a certain hand-hold position. The user must watch a pointer and its associated calibrated scale while applying load to a threaded fastener. Its accuracy is compromised by the parallax between the pointer and the calibrated scale. The dial type wrench is not grip sensitive, but the user must monitor its mechanical dial pointer against a calibrated scale during use. Although fundamentally more accurate, interpretation of the dial display is subject to parallax error. Certain dial wrenches have been fitted with an adjustable preset pointer that contacts the measurement pointer completing an electrical circuit that drives a signaling device, such as a lamp or a buzzer. These electric dial wrenches allow wrench operation without watching the dial.
Mechanical click type wrenches are most common. They provide an audible and tactile signal to the user when a preset torque is reached. The adjustable click types feature a calibrated scale on the body of the wrench and are preset by turning a micrometer type handle grip to the desired torque value. The torque preset scale is often misread on adjustable wrenches due to interpretation between the scale and the handle position. The release mechanism of adjustable click wrenches exhibits a slight reduction in torque at the moment of signal alert that encourages the user to cease applying load. However, this characteristic is diminished at lower torque settings and may be missed altogether by the user. Click wrenches are also hand-hold position sensitive. Most mechanical wrench types have been offered with multiple measurement scales, such as Nm and ft-lb or in-lb and cm Kg.
Because of their improved accuracy, electronic torque wrenches have been traditionally used in more critical applications. Electronic wrenches improve functionality by providing additional measurement features such as, torque tracking, peak reading capture, torque units conversion, data storage, and multiple and early warning presets. The concept of torque-angle (also known as torque-turn) fastener installation was made possible with the introduction of wrenches that could sense both torque and angular rotation. The advent of microelectronics has allowed significant cost reductions in electronic wrench manufacture thereby allowing the advantages of electronic wrench features to be experienced by all torque wrench users. In addition to a digital display of measurement parameters, torque and angle preset signaling has typically been accomplished using lights, sounds and vibrating motors.
Presently available electronic torque wrenches lack the sound and tactile feel of the mechanical click wrench. Although an attempt was made to provide a workable solution in U.S. Pat. No. 6,119,562, a number of disadvantages remain. For example, the sensing element is a part of the release mechanism, which compromises the accuracy and usability of the measurement during and after the release. In addition, the sensor element, being a part of the release mechanism, negates the feasibility of interchangeable drivers. The triggering methods suggested for the release mechanism must be driven into a reset position by the actuator after release.
In addition, angle measuring instruments currently on the market that use gyro or accelerometer technology require the establishment of a “zero point” reference. This is because this type of technology cannot differentiate between rotation on or off the fastener. This causes the sensor to capture an offset that causes the display to drift at a rate that is relative to any motion experienced during the zeroing mode. Therefore, the measurement instrumentation is either held in a state of reset, or is manually reset to zero just prior to actual measurement. Examples include an SPX torque-angle adaptor, as disclosed in U.S. Pat. No. 6,965,835, and an “angle zero set” reference, as disclosed in U.S. Pat. No. 7,565,844, which set a “zero point reference” prior to angle measurement. This generally involves holding the sensing element still for a defined period of time during the power-up function or after pushing a button to initiate the zeroing function. If the operator moves (even slightly) during the zeroing function, the motion will be captured and interpreted as “zero” and added to an actual reading as an offset. More dramatically, if such offset is captured during the zeroing function, and the wrench or adaptor is subsequently held still, the display will begin incrementing or decrementing as though the wrench or adapter were moving.
Because there is no physical zero angle reference for the gyro or accelerometer sensors, existing products cannot include compensation for zero drift. Zero drift of the sensor also causes the display to increment or decrement due to environmental influences, such as temperature and pressure changes, over time. To insure continued accuracy of the angle measurement during use, the products must be manually zeroed by reinitiating the power-on function or by pushing the zeroing button.
Another problem that is frequently experienced by conventional electromechanical torque wrenches relates to the ratcheting motion. The application of torque and angular rotation to a fastener is rarely accomplished in one continuous stroke of a wrench. A ratcheting drive between the wrench and the work allows fastener installation in repeatedly segmented strokes. This facilitates ergonomic as well as workspace clearance limitations. In the measurement of torque and angle parameters during a ratcheting sequence, certain manipulation of the sensed signals must be accomplished. Torque is cumulative in the work. The repeated application of segmented rotation results in higher torque readings for each subsequent stroke. Therefore, the amount of torque applied can be monitored without regard to previous readings. However, for angle measurement, the ratcheting motion is opposite the direction of rotation for fastener installation. Therefore, the accumulation of the angle reading must be noted for the prior stroke, the reverse rotation ignored, and further advancement (at the subsequent applications of rotation) added on.
The present invention significantly improves the functionality of the torque and angle measurements and overcomes the major disadvantages of the prior art.